It is known that pressure variations or pulses may occur when fluids are pumped through conduits. These pressure variations and the resulting mechanical vibrations can disrupt the constant flow of the fluid and cause damage and wear to the pipes and connections. Moreover, such pressure variations can disrupt or ruin downstream applications, which may depend on smooth, steady flow for their proper function. To address these problems, pulse dampeners have been developed to reduce or eliminate pulsations and vibrations in the fluids as they are pumped through pressurized systems. Conventional pulse dampeners typically comprise a chamber or passage that is connected to the pipe or other conduit through which the pressurized fluid flows, and an internal mechanism for absorbing and “dampening” the pulses. Conventional pulse dampeners often use internal elastic membranes which expand and contract in response to pressure changes in the pressurized fluids and thereby absorb pulses as the fluid passes through the dampener and past the membrane.
One major disadvantage of conventional dampeners that use elastic membranes is that often the dampener's pressure tolerance must be sacrificed for low internal volumes, and vice versa. In order for such a conventional dampener to tolerate high pressures (e.g., pressures at or above 100 psi), the elastic membrane typically must be relatively thick to prevent it from ripping or exploding under the pressure. However, thick membranes are relatively insensitive to pulsations, and thus a thick membrane must have a large surface area in order to be an effective dampener. Larger membrane surface areas unfortunately mean greater internal volumes. Conversely, a thin membrane is very sensitive to pressure fluctuations and thus can be kept small resulting in smaller internal volumes while maintaining good dampening results. However, conventional thin membranes often rip at high pressures, meaning that conventional dampeners with thinner membranes cannot tolerate high pressure fluid systems.
To address these problems, methods of compensating for fluid pressure have been developed. One such method is to use air and air pressure to try to counteract and compensate for the pressure exerted by the pressurized fluid moving through the dampener. Conventional pulse dampeners or surge suppressors that do not use elastic membranes have incorporated air chambers such that the fluid being pumped through the conduit is allowed to compress the air in the air chamber and occupy a greater proportion of the volume of the chamber as the fluid pressure increases. When the fluid pressure decreases, the air in the chamber expands and returns some of the fluid from the chamber to the conduit system.
A problem with the above approach using one or more air chambers that communicate with the fluid channel, however, is that some of the air will likely dissolve into the fluid being pumped, thereby reducing the volume of air in the chamber and potentially affecting the composition of the fluid being pumped. An alternative approach that eliminates this problem is to use a dampening membrane that separates the fluid being pumped through the conduit system from an air chamber used to compensate for the fluid pressure. In such systems, the fluid exerts pressure on the membrane, causing it to expand toward the air pressure chamber, and the air in the chamber pushes back on the membrane to compensate for that pressure and membrane displacement. Conventional pulse dampeners that use this method may use a closed air chamber with a static amount of air. However, without the ability to increase or decrease the amount of air in the air chamber, the pressure and volume of the air cannot be independently controlled. As the fluid pressure increases on one side of the membrane, the air in the air chamber on the other side of the membrane is compressed. The air pressure rises, while the volume occupied by the air is reduced. This results in a corresponding increase in the internal volume that must be filled by the fluid. Even more problematic is the fact that as the air volume is compressed, the pulse dampener becomes less and less effective at absorbing pulses because it takes more and more fluid pressure to compress the remaining air by any given amount.
Feedback mechanisms have been developed for use with such dampeners, allowing air to be dynamically added or removed from the air chamber, in response to changes in the fluid pressure. Such feedback mechanisms enable the pressure in the air-chamber to be adjusted, while maintaining a roughly constant volume of air in the chamber. However, conventional feedback mechanisms have several limitations: They tend to be complex and use elaborate mechanical or electromechanical means, making them difficult and expensive to manufacture and maintain.
U.S. Pat. No. 5,797,430 titled “Adaptive Hydropneaumatic Pulsation Dampener,” issued to Beckë et al. on Aug. 25, 1998, for example, uses an air or gas chamber to compensate for the displacement of the dampening membrane by the pressurized fluid. The hydropneumatic pulsation dampener disclosed in the Beckë et al. '430 patent, however, uses the pressurized fluid itself to regulate the air pressure in the gas chamber. The system couples the hydraulic system with a gas chamber such that some of the pressurized fluid is directed into the gas chamber and exerts pressure on a membrane that encloses the gas. When the gas membrane is compressed by the fluid, it pushes air against the dampening membrane. A throttle system regulates how much of the fluid is directed to the gas chamber, depending on changes in pressure in the hydraulic system. Thus, higher fluid pressures, and the greater associated displacement of the dampening membrane toward the gas chamber, result in greater amounts of fluid around the gas chamber membrane, which in turn causes more air pressure to be exerted on the dampening membrane against that of the fluid. Unfortunately, the use of the hydraulic fluid itself to regulate the air pressure in this mechanism creates a huge internal volume because large amounts of the fluid are directed into the gas chamber and out of the hydraulic system.
U.S. Pat. No. 3,741,692, titled “Surge Suppressor for Fluid Lines” and issued to Rupp on Jun. 26, 1973, discloses a surge suppressor that uses as air chamber for auto-compensation and incorporates an inlet/outlet valve system to adjust the air pressure in the air chamber in response to changes in the fluid pressure while maintaining the volume of air in the air chamber. This system uses an axial rod and plungers to open the different valves at the appropriate times, and has a very large air chamber.
Similarly, U.S. Pat. No. 4,556,087, titled “Pulsation Dampener” and issued to Casilli on Dec. 3, 1985, involves a complex mechanical system for independently regulating the pressure and volume of air in the chamber, including a large air chamber, an axial rod connection, and an on/off valve. These types of systems are intended to accommodate extremely large fluid volumes and pressures and are not ideal for a dampener intended to work effectively with relatively small amounts of fluid. They are also mechanically complex and expensive to manufacture.
Another example of a pulse dampener is that disclosed in U.S. Pat. No. 4,629,562, titled “Pulse Dampener” and issued to Kercher on Dec. 16, 1986. The Kercher patent explains that a pulse dampener may be used in a liquid chromatography system and teaches the use of a chemically inert diaphragm and a unitized plug that has two portions, each of which has different compressibility characteristics. However, no pressure feedback or compensation is provided for dampening pulses.
Yet another example of a pulse dampener is that shown in U.S. Pat. No. 4,552,182, titled “Hydraulic Pulse Dampener Employing Two Stiff Diaphragms and Nesting Members,” issued to Graham on Nov. 12, 1985. The Graham patent discloses the use of two diaphragms, each positioned opposite a recess formed in the pulse dampener housing. The two diaphragms are designed so that each will flex under different pressure ranges. However, no pressure feedback or compensation is provided for dampening pulses.
The foregoing U.S. Pat. Nos. 5,797,430, 3,741,692, 4,556,087, 4,629,562, and 4,552,182 are hereby incorporated by reference as if fully set forth herein.